Dosage Forms and Strengths

Contraindications

Metronidazole Gel, 1% is contraindicated in patients with a history of hypersensitivity to metronidazole or to any other ingredient in the formulation.

Warnings and Precautions

Neurologic Disease

Peripheral neuropathy, characterized by numbness or paresthesia of an extremity has been reported in patients treated with systemic metronidazole. Although not evident in clinical trials for topical metronidazole, peripheral neuropathy has been reported with the post approval use. The appearance of abnormal neurologic signs should prompt immediate reevaluation of Metronidazole Gel, 1% therapy. Metronidazole should be administered with caution to patients with central nervous system diseases.

Blood Dyscrasias

Metronidazole is a nitroimidazole; use with care in patients with evidence of, or history of, blood dyscrasia.

Contact Dermatitis

Irritant and allergic contact dermatitis have been reported. If dermatitis occurs, patients may need to discontinue use.

Eye Irritation

Topical metronidazole has been reported to cause tearing of the eyes. Avoid contact with the eyes.

Adverse Reactions

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
In a controlled clinical trial, 557 patients used Metronidazole Gel, 1% and 189 patients used the gel vehicle once daily for up to 10 weeks. The following table summarizes selected adverse reactions that occurred at a rate of ≥1%:

Table 1: Adverse Reactions That Occurred at a Rate of ≥1%

System Organ Class/Preferred Term

Metronidazole Gel, 1%

Gel Vehicle

N= 557

N= 189

Patients with at least one AE
Number (%) of Patients

186 (33.4)

51 (27.0)

Infections and infestations

76 (13.6)

28 (14.8)

Bronchitis

6 (1.1)

3 (1.6)

Influenza

8 (1.4)

1 (0.5)

Nasopharyngitis

17 (3.1)

8 (4.2)

Sinusitis

8 (1.4)

3 (1.6)

Upper respiratory tract infection

14 (2.5)

4 (2.1)

Urinary tract infection

6 (1.1)

1 (0.5)

Vaginal mycosis

1 (0.2)

2 (1.1)

Musculoskeletal and connective tissue disorders

19 (3.4)

5 (2.6)

Back pain

3 (0.5)

2 (1.1)

Neoplasms

4 (0.7)

2 (1.1)

Basal cell carcinoma

1 (0.2)

2 (1.1)

Nervous system disorders

18 (3.2)

3 (1.6)

Headache

12 (2.2)

1 (0.5)

Respiratory, thoracic and mediastinal disorders

22 (3.9)

5 (2.6)

Nasal congestion

6 (1.1)

3 (1.6)

Skin and subcutaneous tissue disorders

36 (6.5)

12 (6.3)

Contact dermatitis

7 (1.3)

1 (0.5)

Dry skin

6 (1.1)

3 (1.6)

Vascular disorders

8 (1.4)

1 (0.5)

Hypertension

6 (1.1)

1 (0.5)

Table 2: Local Cutaneous Signs and Symptoms of Irritation That Were Worse Than Baseline

Metronidazole Gel, 1%

Gel Vehicle

Sign/Symptom

N= 544

N= 184

Dryness

138 (25.4)

63 (34.2)

Mild

93 (17.1)

41 (22.3)

Moderate

42 (7.7)

20 (10.9)

Severe

3 (0.6)

2 (1.1)

Scaling

134 (24.6)

60 (32.6)

Mild

88 (16.2)

32 (17.4)

Moderate

43 (7.9)

27 (14.7)

Severe

3 (0.6)

1 (0.5)

Pruritus

86 (15.8)

35 (19.0)

Mild

53 (9.7)

21 (11.4)

Moderate

27 (5.0)

13 (7.1)

Severe

6 (1.1)

1 (0.5)

Stinging/burning

56 (10.3)

28 (15.2)

Mild

39 (7.2)

18 (9.8)

Moderate

7 (1.3)

9 (4.9)

Severe

10 (1.8)

1 (0.5)

The following additional adverse experiences have been reported with the topical use of metronidazole: skin irritation, transient redness, metallic taste, tingling or numbness of extremities, and nausea.

Post Marketing Experience

The following adverse reaction has been identified during post approval use of topical metronidazole: peripheral neuropathy. Because this reaction is reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate the frequency or establish a causal relationship to drug exposure.

Drug Interactions

Oral metronidazole has been reported to potentiate the anticoagulant effect of coumarin and warfarin, resulting in a prolongation of prothrombin time. Drug interactions should be kept in mind when Metronidazole Gel, 1% is prescribed for patients who are receiving anticoagulant treatment, although they are less likely to occur with topical metronidazole administration because of low absorption.

USE IN SPECIFIC POPULATIONS

Pregnancy

Teratogenic Effects: Pregnancy Category B.

There are no adequate and well-controlled studies with the use of Metronidazole Gel, 1% in pregnant women. Metronidazole crosses the placental barrier and enters the fetal circulation rapidly. No fetotoxicity was observed after oral administration of metronidazole in rats or mice at 200 and 20 times, respectively, the expected clinical dose. However, oral metronidazole has shown carcinogenic activity in rodents. Because animal reproduction studies are not always predictive of human response, Metronidazole Gel, 1% should be used during pregnancy only if clearly needed.

Nursing Mothers

After oral administration, metronidazole is secreted in breast milk in concentrations similar to those found in the plasma. Even though blood levels taken after topical metronidazole application are significantly lower than those achieved after oral metronidazole a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother and the risk to the infant.

Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

Geriatric Use

Sixty-six subjects aged 65 years and older were treated with Metronidazole Gel, 1% in the clinical study. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

Overdosage

There are no reported human experiences with overdosage of Metronidazole Gel, 1%. Topically applied metronidazole can be absorbed in sufficient amount to produce systemic effects.

Metronidazole Gel Description

Metronidazole Gel, 1% contains metronidazole, USP. Chemically, metronidazole is 2-methyl-5-nitro-1 H-imidazole-1-ethanol. The molecular formula for metronidazole is C6H9N3O3. It has the following structural formula:

Metronidazole has a molecular weight of 171.16. It is a white to pale yellow crystalline powder. It is slightly soluble in alcohol and has solubility in water of 10 mg/mL at 20˚C. Metronidazole belongs to the nitroimidazole class of compounds.

Metronidazole Gel - Clinical Pharmacology

Mechanism of Action

The mechanism of action of metronidazole in the treatment of rosacea is unknown.

Pharmacodynamics

The pharmacodynamics of metronidazole in association with the treatment of rosacea are unknown.

Pharmacokinetics

Topical administration of a one gram dose of Metronidazole Gel,1% to the face of 13 patients with moderate to severe rosacea once daily for 7 days resulted in a mean ± SD Cmax of metronidazole of 32 ± 9 ng/mL. The mean ± SD AUC(0-24) was 595 ± 154 ng*hr/mL. The mean Cmax and AUC(0-24) are less than 1% of the value reported for a single 250 mg oral dose of metronidazole. The time to maximum plasma concentration (Tmax) was 6-10 hours after topical application.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

Metronidazole has shown evidence of carcinogenic activity in a number of studies involving chronic, oral administration in mice and rats, but not in studies involving hamsters.
In several long-term studies in mice, oral doses of approximately 225 mg/m2/day or greater (approximately 37 times the human topical dose on a mg/m2 basis) were associated with an increase in pulmonary tumors and lymphomas. Several long-term oral studies in the rat have shown statistically significant increases in mammary and hepatic tumors at doses >885 mg/m2/day (144 times the human dose).
Metronidazole has shown evidence of mutagenic activity in several in vitro bacterial assay systems. In addition, a dose-related increase in the frequency of micronuclei was observed in mice after intraperitoneal injections. An increase in chromosomal aberrations in peripheral blood lymphocytes was reported in patients with Crohn's disease who were treated with 200 to 1200 mg/day of metronidazole for 1 to 24 months. However, in another study, no increase in chromosomal aberrations in circulating lymphocytes was observed in patients with Crohn's disease treated with the drug for 8 months.
In one published study, using albino hairless mice, intraperitoneal administration of metronidazole at a dose of 45 mg/m2/day (approximately 7 times the human topical dose on a mg/m2/day basis) was associated with an increase in ultraviolet radiation-induced skin carcinogenesis. Neither dermal carcinogenicity nor photocarcinogenicity studies have been performed with METROGEL or any marketed metronidazole formulations.

Clinical Studies

In a randomized, vehicle-controlled trial, 746 subjects with rosacea were treated with Metronidazole Gel, 1% or gel vehicle once daily for 10 weeks. Most subjects had “moderate” rosacea at baseline. Efficacy was determined by recording reduction in inflammatory lesion counts and success rate in the Investigator Global Assessment (percentage of subjects “clear” and “almost clear” of rosacea at the end of the study). The scale is based on the following definitions:

Table 3: Investigator Global Assessment Scale

Score

Grade

Definition

0

Clear

No signs or symptoms present; at most, mild erythema

1

Almost Clear

Very mild erythema present. Very few small papules/pustules

2

Mild

Mild erythema. Several small papules/pustules

3

Moderate

Moderate erythema. Several small or large papules/pustules, and up to 2 nodules

4

Severe

Severe erythema. Numerous small and/or large papules/pustules, up to several nodules

Subjects treated with Metronidazole Gel, 1% experienced a mean reduction of 9.4 inflammatory lesions in the Week-10 LOCF group, compared to a reduction of 5.6 for those treated with vehicle, or a difference in means of 3.8 lesions.

The contribution to efficacy of individual components of the vehicle has not been established.

How Supplied/Storage and Handling

Metronidazole Gel, 1% is clear, colorless to pale yellow in color, and is supplied as follows: